It consists of a count of ticks of type Rep and a tick period, where the tick period is a compile-time rational constant representing the number of seconds from one tick to the next.

The only data stored in a duration is a tick count of type Rep. If Rep is floating point, then the duration can represent fractions of ticks. Period is included as part of the duration's type, and is only used when converting between different durations.

Note: each of the predefined duration types up to hours covers a range of at least ±292 years.

Each of the predefined duration types days, weeks, months and years covers a range of at least ±40000 years. years is equal to 365.2425 days (the average length of a Gregorian year). months is equal to 30.436875 days (exactly 1/12 of years).